I don’t know the specifics of the costs of caring for one with DMD, but I strongly agree that in general, new disease therapies are the only sure way to drive down medical costs in the medium and long term. This represents a victory, no doubt.
[^1] see FDA press release and monograph. addditional doses won't do much because by then the immune system has learned to attack the AAV vector -- a different vector strain would be needed and that would be a new drug to be approved
[^2] no idea what the turnover rate is. and honestly, the FDA isn't even sure it helps with anything, hence conditional.